The use of ophthalmic lenses for the correction of ametropia is well known. For example, multifocal lenses, such as progressive addition lenses (“PALs”), are used for the treatment of presbyopia. The progressive surface of a PAL provides far, intermediate, and near vision in a gradual, continuous progression of increasing dioptric power from far to near focus.
Presbyopia results from a decrease in the eye's ability to focus near objects. This decrease is believed to be due to one or both of hardening of the lens and weakening of the ciliary muscle. Presbyopia results in a decrease in the individual's ability to read small print. Additionally, as one ages there is a decrease in the retina's ability to resolve fine detail in a focused image.
Resolution can be improved by magnification. However, conventional PALs provide only a fixed magnification that is based on the lens power. Thus, an individual may have spectacle lenses that provide the appropriate add power to enable the individual to read small print, but the lenses will not provide the magnification necessary the achieve the desired resolution. If the eye care professional increases the individual's add power prescription by 0.25 diopters (“D”) to provide them with a increased magnification, this results in an increase in image blur or defocus.
It is known to provide magnification for an individual based on an approximation of the magnification required. For example Kestenbaum's Rule, in which dividing the distance vision numerator by the denominator provides an approximation of the magnification required for reading Jaeger 5, is known. This, and other known methods for providing increased magnification are disadvantageous in that they require changes in the lens' power to increase magnification, thus altering the position of best focus. Thus, there exists a need for providing magnification without changing the dioptric power of the lens.